Method of electrocoating electric wire

ABSTRACT

This invention relates to electric wire with a double coating made by producing a first layer of a water dispersion varnish by electrophoresis and then a second layer of a water-soluble varnish by electrophoresis with subsequent baking, and a method of manufacturing such wire and an apparatus for the coating. It includes also the step of treating the first layer with an organic solvent or a mixture of water and an organic solvent soluble in water between the steps of coating the first layer and the second layer.

United States Patent Masuda et al.

[ June 24, 1975 1 METHOD OF ELECTROCOATING FOREIGN PATENTS R APPLICATIONS ELECTRIC WIRE |,08l,767 8/1967 United Kingdom I 304/181 [75] Inventors: Shigeo Masuda, Osaka; Toshihiko Tanaka, Nagoya, both of Japan OTHER PUBLICATIONS [73] Asslgneez guniitonjio Electric Industries, Ltd., Hagan Journal of Paint Technology, (Aug. .66) N0 499, v01. 38, pp. 436 & 437. [22] Filed: Feb. [1, 1971 [2|] Appl. N 1 .475 Primary Examiner-Howard S. Williams Foreign Application Priority Data Attorney, Agent, or FirmCarothers & Carothers Feb. 14. 1970 Japan -12443 [57] RACT 45-7 646 Aug [970 Japan 2 This mvention relates to electric wire with a double 52 us. c1 .1 204/181; 204/181 coating made by Producing a first layer of a water 51 Int. Cl 801k 5/02 Persion varnish y electrophoresis and then a Seoond [58] Field of Search 204/l8l, 300 15c layer of a wateesoluble varnish y electrophoresis with subsequent baking, and a method of manufactur- 56] References Cited ing such wire and an apparatus for the coating. It in- UNITED STATES PATENTS cludes also the step of treating the first layer with an organic solvent or a mixture of water and an organic Mormon solvent soluble in water between the steps of coating 3:540:990 H970 204" the first layer and the second layer. 3,547.788 l2/l970 Tanaka ct al. 204/l8l 3,681,224 8/1972 Stromberg .7 204/181 2 Claims, 3 Drawing Figures WA me D/JPns/a/v WA r52 /04: W4 re: uAJlE vA/zmsu ORGAN/C250! m0 VARNIJH METHOD OF ELECTROCOATING ELECTRIC WIRE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to insulated electric wire made by an electrophoretic coating method, and its manufacturing method and coating apparatus.

2. Description of Prior Art In recent years much activity has been made in research and development concerning the method of manufacturing magnet wire by electrophoretic coating in which a water varnish is applied to a conductor by electric energy and is then baked, and which is different from the well-known conventional method in which a suitable quantity of a varnish is applied to a conductor by means of a die, wiper roller, felt, etc., and then is baked.

In connection with the method of manufacturing magnet wire by electrophoretic coating, two cases may be considered from the viewpoint of the water varnish material used.

One case is where a water-soluble varnish is applied as a water varnish, and the other case is where a water dispersion varnish is applied.

When a water-soluble varnish is used for the electrophoretic coating, the appearance of the coating film of the insulated electric wire obtained is glossy and smooth, but the coating has a drawback in that it does not readily satisfy the characteristics required of the electric wire. That is to say, if a water-soluble varnish is applied to a conductor, the electrodeposited film shows a great insulation resistance, so that the coating of a thick film cannot be made. Besides, there is a limit to the molecular weight of the resin if the varnish is made soluble in water, and furthermore it may be necessary to introduce into the molecular structure a hydrophilic group such as the carboxyl group, hydroxide group, etc. At the present time such a coating cannot satisfy the characteristics required of electric wire because of its molecular structure.

In the case of a water dispersion varnish, it can be applied to any desired thickness, unlike a water-soluble varnish. When it is baked, however, the coating film lacks a glossy appearance and may have cracks, so that it is not suitable for use on magnet wire.

The conditions being as mentioned above, the electric wire is produced with a glossy surface when a water dispersion varnish is used by adding to the varnish an organic solvent which dissolves the dispersed resin, or by passing the wire after the electrodeposition coating through an organic solvent which swells and dissolves the electrodeposited resin as taught by French Pat. No. 1,52 l ,454, or by spraying it by means of a spray gun or the like or by passing the wire through the vapor of an organic solvent.

BRIEF DESCRIPTION OF THE DISCLOSURE An object of this invention is to obtain an excellent insulated electric wire, and, more particularly, to obtain an excellent electric wire with an electrodeposited coating not heretofore obtainable.

Another object of this invention is to obtain a method of manufacturing an excellent electric wire with an electrodeposited coating as mentioned above, and to obtain an apparatus therefor.

Still another object of this invention is to obtain such a manufacturing method and apparatus as mentioned above which are capable of operation for a long time and are valuable for industrial purposes.

BRIEF EXPLANATION OF THE DRAWINGS FIG. 1 is a diagrammatic view showing an embodiment of this invention.

FIG. 2 is a diagrammatic view showing another embodiment of this invention.

FIG. 3 is a diagrammatic view showing an embodiment of this invention which is made capable of operation for a long time.

DETAILED DESCRIPTION OF THE INVENTION The method of this invention represents a success in an effort to combine the aforementioned water dispersion varnish and water-soluble varnish to have them mutually make up for the shortcomings of each other and display their merits only. This success has made it possible to obtain electric wire which has any desired coating film and which provides a surface in good condition.

Generally, if electrodeposition is made with a water dispersion varnish, the electrodeposited film (wet film) has electric conductivity. If a water-soluble varnish is electrodeposited, however, the electrodeposited film has a high insulating property (approximately 10" l0 Q'cm). The manufacturing method of this invention is made by combining such properties of the two.

That is is say, magnet wire having a desired film thickness and a good surface condition is obtained by first electrodepositing a water dispersion varnish on a conductor and then overcoating it with a water-soluble varnish. The resin used for the overcoating makes up for the defects of the film of the water dispersion varnish used for the undercoating. The problems of luster, cracks, etc., of the film made of a water dispersion varnish are solved in this way.

Insulated electric wire having desired special advantages can be obtained by suitably selecting the material for the water-soluble varnish used for the overcoating. For example, insulated electric wire having great resistance to wear, insulated electric wire having excellent resistance to solvents and chemicals, etc., may be obtained.

As water-soluble varnish, a varnish produced by dissolving in water a resin whose principal component is alkyd, polyester, melaminester, acryl ester, epoxy ester, acrylonitrile, etc., may be used. Although water is the principal solvent used for such water-soluble varnish, an organic solvent miscible with water may also be used. Such organic solvents are, for example N, N- dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrolidon, etc. The concentration of the resin in water-soluble varnish used for the overcoating may be I 40 percent, but is preferably about 5 15 percent.

For the water dispersion varnish, a resin whose principal component is acrylonitrile, polyethylene, polytetrafluoroethylene, trifluoride resin, polyurethane, epoxy-polyamide, styrene-butadien copolymer, styrene-acrylonitrile copolymer, vinyl ether, acetateethylene copolymer or acrylic acid ester resins of various kinds, is dispersed in water. In some cases, an emulsifier, catalyst, etc., may be used. For example, Lectone (a trade name) made by DuPont, a water dispersion of acrylonitrile made by Nitto Denko Kabushiki Kaisha, etc., are used.

The resins on these water soluble varnishes and water dispersion varnishes are generally charged or ionized negative, but not always negative. Some of them may be charged or ionized positive. With respect to the var nishes to be used for the coating according to this invention, there are four possible combinations from the electrical application. That is to say, there are the four possible cases where both the water dispersion varnish and watersoluble varnish are positive, where both of them are negative, where the water dispersion varnish is positive and the watersoluble varnish is negative and where the water dispersion varnish is negative and the watersoluble varnish is positive.

Manufacture in any of these cases can be made by suitably selecting the polarity of the conductor and electrode.

The electrophoretic coating method according to this invention will be explained in further detail. Since a resin is to be electrodeposited further on the resin electrodeposited in the first bath, it is preferable with respect to the apparatus and power source used that the electrophoretic baths are arranged in series and electric circuits connected in series as shown in FIG. I.

The electrophoretic baths are provided at least with a varnish control tank and a pump. In the first bath a varnish is placed which will provide electrodeposited resin having electric conductivity. With respect to the varnish placed in the second bath, it does not matter whether the resin electrodeposited has electric conductivity or not. The power source to be used is a direct current source, and it is preferable that the desired electric current can branch into both baths. It is advisable to insert a variable resistor for this purpose.

The apparatus for the electrophoretic coating will be explained, with reference to the drawing.

1 denotes the conductor. It proceeds in the direction shown by the arrow. The conductor travels through slits made in the walls of the baths, and proceeds to the baking furnace without having the electrodeposited resin deformed or peeled off.

2, 3, 2 make up the first bath. 2 denotes the troughs which receive the liquid which has overflowed through the slits of the electrophoretic bath. The varnish in 2 goes back to the electrophoretic bath 3 via the varnish control tank 5 by the action of the pump 6. Likewise, 7, 8, 7 make up the second bath.

7 denotes the troughs which receive the liquid which has overfiowed through the slits of the electrophoretic bath 8.

The varnish in 7 goes back to the electrophoretic bath 8 via the varnish control tank 10 by the action of the pump 11.

4 and 9 denote electrodes provided in the baths respectively.

The conductor which has been coated by electrophoresis in 3 and 8 is baked in the baking furnace l2.

l3 denotes the direct current source, and 13-1, 13-2, ammeters for measuring electric currents flowing in the first and the second bath. A desired film thickness will be obtained by controlling the value of these electric current. 13-3 denotes a variable resistor installed for varying the electric currents flowing in A A in order to change the values of these currents as desired.

The wiring of the circuits will be as shown in the Figure so that the first bath and the second bath may have circuits in series with respect to the direct current source. The variable resistor is installed on the side where the liquid relative resistance plus the coated film resistance is smaller.

FIG. 1 shows an instance where the conductor is positive and the electrodes in the baths are negative, namely an instance where the resin is charged negative. In case the resin is charged positive, it is all right if the conductor is made negative and the electrodes in the baths positive.

The above-described method is the best one. As an alternative, however, electric charging may be done by circuits as shown in FIG. 2. That is to say, the electrode 4 provided in the bath 3 and the conductor 1 are connected at the position 13, namely at the position before the entry of the conductor into the bath, to form a circuit, while the electrode 9 provided in the bath 4 and the conductor are connected to form a circuit, both being charged with direct current.

In this case, there are three ways to connect the electrode 9 and the conductor. One of them is as made at the position 14, as shown in FIG. 2. Since E is generally of a higher voltage than E however, the current which comes from E is liable to flow back toward E, in this case. This is prevented by the installation of a diode 18. Another way is one in which the connection is made at the position 15. In this case there takes place a drawback in that the film formed in the first bath 3 is apt to come off. The third way is one in which the connection is made at the position of the take-up machine 16. In this case, the film coating at the end portion of the conductor is removed when starting the take-up to produce a contact between the conductor and the power source and connect the bared conductor with the power source at that point.

This way of connection is effective when electrodeposition is made by having electric currents of opposite polarities flow in the circuits in case the polarity of the charge on the resins in the first bath 3 and the second bath 8 is different, namely in case one is negative and the other is positive.

As has been stated, excellent insulated electric wire which cannot be obtained by the electrodeposition of a single varnish has been obtained by using a combination of a water dispersion varnish and a water-soluble varnish, the former being electrodeposited for the under-layer and the latter for the outer-layer.

The above objective has been attained by a method as described below.

A treating bath is provided between the first bath and the second bath. By treating the electrophoretic coating film produced on the conductor in the first bath with a organic solvent or a mixture of water and a water-soluble organic solvent, in this treating bath, varnish remaining on the film of electrophoretic coating in the first bath is removed to prevent the deterioration of the varnish in the second bath. At the same time, the film of the coating in the first bath is swollen and wetted by the organic solvent or its mixture with water used as a treating liquid and is given a greater bond with the film coating in the second bath. Insulated electric wire with a double coating which has excellent properties can thus be obtained.

When treating the wet filrn with a liquid, it is preferable to use the liquid at a temperature of about 60 C to make the treatment more effective.

An embodiment of this invention will be explained in detail with reference to the drawing. An embodiment as shown in FIG. 2 in provided with a treating bath as shown in FIG. 3. Numerals 1 17 refer to the same things in each of the figures. 1 denotes the conductor. 2, 3, 2 make up the first bath, and 7, 8, 7 the second bath. 19, 20, 19 make up the treating bath. They respectively consist of main bodies 3, 8 and and parts 2, 7, and 19 for receiving liquid flowing out through the slits in the walls of the main bodies. 4, 9 denote electodes. 5, 10 and 21 are control tanks respectively, and 6, 11, 22 pumps. E and E denote direct current power sources, and 18 a diode for the prevention of back flow.

For instance, a water dispersion varnish is put in the first bath 2, 3, 2, and a water soluble varnish is put in the second bath 7, 8, 7. A treating liquid of an organic solvent or a mixture of an organic solvent with water, is put in the treating bath 19, 20, 19. The liquid flows through the slits and circulates through the tanks 5, l0, 2] by means of the pumps, so that it is always present in the baths.

The conductor 1 enters the first bath 2, 3, 2 where a dispersion varnish is electrodeposited thereon. It then enters the treating bath 19, 20, 19 where treatment is made for the removal of sticking varnish, swelling of the film, etc., and it then enters the second bath 7, 8, 7 where a water soluble varnish is electrodeposited on the coating. lt thereafter enters the baking furnace 12, where baking is done and insulated electric wire with a double coating is obtained.

An instance will be explained, wherein the method of FIG. 2 provides no treating bath. lOO liters of a watersoluble varnish was used in the second bath, and the operation was was made with 30 conductors moved at a line speed of 50 m/sec. in about 3 6 hours, the varnish in the first bath would get in the second bath and the varnish in the second bath deteriorated, the concentration of the varnish of the first bath contained in the second bath becoming even 4 5 percent. That is to say, continuous operation was possible only for about 3 6 hours. If the operation was continued for a longer time, the surface of the electrodeposited layer lacked luster, so that it became impossible to obtain good magnet wire.

Now, however, when a treating bath was provided and the aforementioned treating liquid was used therein, the properties of the coating film of the electric wire were improved and at the same time it was possible to carry out continuous operation for 24 hours or more under the same manufacturing conditions as already mentioned.

The treating liquid used in this application is water, an organic solvent, or a mixed liquid of water and a water-soluble organic solvent. Preferably, as a watersoluble organic solvent, dimethylformamide, dimethylacetamide, pyrolidon, ethyleneglycol, alkylmono-ether or diethyleneglycol, diacetonealcohol, etc., for example, may be used. It is particularly preferable to use an aqueous solution containing 0 30 percent (concentration percent), especially 1 10 percent (concentration percent), of such a substance.

Instances where insulated electric wire is manufactured by the electrophoretic coating of water dispersion varnish and water-soluble varnish have been explained. However, the present application should not be limited to this combination. Although it is most remarkably effective with the combination of water dispersion varnish and water-soluble varnish, it is applicable to the manufacture of insulated electric wire with any double coating by electrophoresis.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments will now be shown, but this intention is not limited to these embodiments.

Example for Comparison 1 The bath is filled with an acrylonitrile varnish whose main component is water dispersion varnish of acrylonitrile, adjusted to a concentration of 7 percent and a pH of 8.0. Copper wire of a 1 mm diameter is used as the conductor. A voltage is applied between it and a cathode provided in the bath, and the acrylonitrile resin is deposited on the conductor by flowing electric current. The manufacturing conditions and the properties obtained are as shown in the Table.

Example of Comparison 2 The bath is filled with a tetrafluoride resin varnish, whose principal component is a water dispersion varnish tetrafluoride resin, adjusted to a concentration of IO percent of a pH of 8.2. Nickel-plated copper wire of a 1 mm diameter is used as the conductor. A voltage is applied between it and a cathode provided in the bath, and tetrafluoride resin is deposited on the conductor by flowing electric current. The manufacturing conditions and the properties obtained are as shown in the Table.

Example for Comparison 3 The bath is filled with a polyvinylformal varnish, whose principal component is a water-soluble varnish polyvinylformal, adjusted to a concentration of IO percent and a pH of 7.7. Copper wire of a 1 mm diameter was used as the conductor. A voltage was applied between it and a cathode provided in the bath, and the polyvinylformal was deposited on the conductor.

The manufacturing conditions and the properties obtained are as shown in the Table.

Example for Comparison 4 The bath is filled with a phenolester water-soluble varnish, whose principal component are water-soluble varnishes bisphenol A and glycol ester, adjusted to a concentration of l0 percent and a pH of 7.8.

Copper wire of a 1 mm diameter is used as the conductor. A voltage was applied between it and a cathode provided in the bath, the phenol ester resin was deposited on the conductor.

The manufacturing conditions and the properties obtained are as shown in the Table.

Example for Comparison 5 Embodiment l Using such baths as shown in FIG. 1, the first bath was filled with the acrylonitrile water dispersion varnish used in the Example for Comparison 1, and the second bath with the water-soluble polyvinylformal varnish used in the Example for Comparison 3. Cathodes were provided in the first and second baths, and a voltage was applied between them and the conductor of copper wire I mm in diameter.

Since the electric current flowing in the first bath and the electric current flowing in the second bath are different because of the respective specific resistances of the liquids and the film resistance, a variable resistor was installed as shown in the Figure. This makes it possible to control the electric current values.

The manufacturing conditions and the properties obtained are as shown in the Table.

Embodiment 2 Baths as shown in FIG. 1 were used. The first bath was filled with the acrylonitrile water dispersion varnish used in the Example for Comparison 1 and the second bath with the water-soluble phenol ester varnish used in the Example for Comparison 4. Cathodes were provided in the first bath and the second bath, and a voltage was applied between them and the conductor of copper wire 1 mm in diameter. Since the electric current flowing in the first bath and the electric current flowing in the second bath are different because of the respective specific resistances of the liquids and film resistance, the value of electric current flowing in each bath is controlled by installing a variable as shown in the Figure.

The manufacturing conditions and the properties obtained are as shown in the Table.

Embodiment 3 Baths as shown in FIG. 1 were used. The first bath was filled with the acrylonitrile water. dispersion varnish used in the Example for Comparison 1 and the second bath with the water-soluble methyacrylic acid varnish used in the Example for Comparison 5. Cathodes were provided in the first and second baths, and a voltage was applied between them and the conductor of copper wire 1 mm in diameter.

Since the electric current flowing in the first bath and the electric current flowing in the second bath are different becauseof the respective specific resistances of the liquids and film resistance, a variable resistor is used as shown in the Figure in order to control the currents which flow.

The manufacturing conditions and the properties obtained are as shown in the Table.

Embodiment 4 Using baths as shown in FIG. 1, the first bath was filled with the tetrafluoride resin water dispersion varnish used in the Example for Comparison 2 and the second bath with the water-soluble polyvinylformal varnish used in the Example for Comparison 3. Cathodes were provided in the first and second baths and a voltage was applied between them and the conductor of nickel-plated copper wire 1 mm in diameter.

Since the electric current flowing in the first bath and the electric current flowing in the second bath are different because of the specific resistance of the liquid and film resistance, the values of the electric currents can be controlled to suit the purpose in mind by installing a variable resistor as shown in the Figure.

The manufacturing conditions and the properties obtained are as shown in the Table.

Embodiment 5 Using baths as shwon in FIG. 1, the first bath was filled with the tetrafluoride resin water dispersion varnish used in the Example for Comparison 2 and the second bath with the water-soluble phenol ester varnish as used in the Example for Comparison 4. Cathodes were provided in the first and second baths, and a voltage was applied between them and the conductor of nickelplated copper wire l mm in diameter.

Since the electric current flowing in the first bath and the electric current flowing in the second bath are different because of the specific resistance of the liquid and film resistance, the values of the electric currents are controlled to suit the desired thicknesses of the films by installing a variable resistor as shown in the Figure.

The manufacturing conditions and the properties obtained are as shown in the Table.

Embodiment 6 Using baths as shown in FIG. 1, the first bath was filled with a tetrafluoride water dispersion varnish used in the Example for Comparison 2 and the second bath with the water-soluble methacrylic acid varnish used in the Example for Comparison 5. Cathodes were provided in the first and second baths, and a voltage was applied between them and the conductor of nickelplated copper wire. Since the electric current flowing in the first bath and the electric current flowing in the second bath are different because of the specific resistance of the liquid and the specific resistance of the electrodeposited film, the electric currents flowing can be controlled to suit the desired thicknesses of the films by installing a variable resistor as shown in the Figure.

The manufacturing conditions and the properties obtained are as shown in the Table.

Example of Comparison 6 The device as shown in the drawing was used. The first bath was filled with a water dispersion varnish whose principal component was acrylonitrile, adjusted to a concentration of 10 percent and a pH of 8.0, and a second bath was filled with a water-soluble varnish whose principal component was acrylic acid ester, ad justed to a concentration of 10 percent and a pH of 7.8. Nothing was put in the treating bath.

The conductor used was a copper wire having a I mm diameter. Electric current of mA was caused to flow in the first bath and electric current of I50 mA in the second bath. Insulated electric wire with a double coatin g film was obtained by carrying out electrophoresis as mentioned above and then baking was performed.

In this case, continued operation for a period over 6 hours was impossible because of the deterioration of the varnish in the second bath.

Embodiment 7 With the treating bath in the Example for Comparison 6 filled with water, insulated electric wire with double coating film was manufactured in the otherwise same way as the Example for Comparison 6.

The varnish in the second bath did not readilydeteriorate, so that continuous operation for more than 24 hours was possible. The insulated electric wire obtained was glossy and had satisfactory properties.

Embodiment 8 With the treating bath in the Example for Comparison 6 filled with 20 percent pyrolidon solution, insulated electric wire with a double coating film was manufactured in the otherwise same way as the Example for Comparison 6. The varnish in the second bath did not readily deteriorate, so that continuous operation for more than 24 hours was possible. The insulated electric wire obtained was glossy and had satisfactory properties.

Embodiment 9 With the apparatus shown in the drawing in use, the first bath was filled with water dispersion varnish, whose principal component was acrylonitrile, adjusted to a concentration of percent of a pH of 8.0. The second bath was filled with a water-soluble phenol ester varnish, whose principal components were bisphenol A and glycol ester. The treating bath was filled with 30 percent pyrolidon solution. The electric current flowing in the first bath was 60 mA and that in the second bath 200 mA. Electrophoretic coating was thus made on a conductor of cooper wire 1 mm in diameter and then baking was done to obtain insulated electric wire with a double coating film. In this case continuous operation for more than 24 hours was possible and insulated electric wire with a double coating film having good properties was obtained.

nish of polyvinylformal with an addition of crotonic acid.

The treating bath was filled with 20 percent dimethylformamide. With the conductor of copper wire 1 mm in diameter in use, electrophoretic coating was carried out with an electric current of 80 mA flowing in the first bath and 180 mA current in the second bath, and then baking was done. Insulated electric wire with a double coating film having a good appearance and good electric wire properties was thus obtained. Continuous operation of at least 24 hours was possible, the varnish in the second bath not deteriorating.

Embodiment l l The first bath was filled with a water dispersion varnish whose principal component was acrylonitrile, adjusted to a concentration of 10 percent and a pH of 8.0, and the second bath was filled with a water dispersion varnish whose principal components were acrylonitrile and acrylic acid ester, adjusted to a concentration of 12 percent and a pH of 7.8. The electric current flowing in the first bath was 65 mA and that in the second bath 45 mA. The conductor used was copper wire 1 mm in diameter. In this case, continuous operation was no longer possible after about 7 hours.

A treating bath filled with percent aqueous solution of pyrolidon was provided. with the other conditions being the same. Then it was found possible to continue the operation for more than 24 hours, and the insulated electric wire with a double coating film obtained had satisfactory properties.

Example for 2 n 3 H 4 H 5 Example H 2 .1 3 n 4 H 5 n 6 Compari- 1 son I Resin (under coat Acrylo- Pol te- Poly- Phenol- Meth- Acrylo Acrylo- Acrylo- Polytet- (over coal} nitrile tra uvinylester acrylic nitrile nitnle nitrrle rafluooroethformal acid Poly- Phenol- Methroethyylene vinylester acrylic lene Melhformal acid Poly- Phenol acrylvinylester ic formal Acid Backing speed (m/min) 20 20 20 20 20 20 20 20 20 20 20 Voltage (V) 8 3 I7 45 60 I4 30 I5 25 25 Current (Al) (mA) 80 60 200 I 50 50 30 35 40 (Ag) (mA) 30 I00 30 I10 l00 Backing temp. (C) 400 470 400 400 400 400 400 400 470 470 470 Outside view crack crack 0 O O O O O O O 0 Diameter of bare wire (qbmm) l l l l 1 l l l l l l Film thickness (a) 40 30 l0 l l 12 30+4 25+5 25+6 25+5 27-4-5 30+6 Pinhole (peace/m) uncountl l l0 l2 l0 0 O 0 0 0 0 able for crack Cut through temp. 240 I50 I70 I55 240 255 255 360 350 340 (load. 5 kg) (C) Abrasion resistance 23 l0 l5 l3 9 30 27 25 l5 13 I1 (600 g) Break down voltage i500 2500 2 I00 2700 2400 8000 9000 8000 6500 7500 7000 Embodiment 10 We claim:

With the apparatus shown in the drawing in use, the

first bath was filled with a water dispersion varnish 65 whose principal component was polyvinylformal, adjusted to a concentration of l 1 percent and a pH of 8.2, and the second bath was filled with a water-soluble varl. The method of manufacturing insulated electric wire comprising the steps of coating a conductor with a water dispersion varnish by electrophoresis, then treating the film coating with a liquid selected from the group consisting of an organic solvent and a mixed liquid of water and water-soluble organic solvent, and further coating the conductor with a water-soluble varnish coated wire in a treating bath of a liquid selected from the group consisting of an organic solvent, and a mixed liquid of water and a water-soluble organic solvent, and applying a second electrophoretic coating in a second electrophoretic bath. 

1. THE METHOD OF MANUFACTURING INSULATED ELECTRIC WIRE COMPRISING THE STEPS OF COATING A CONDUCTOR WITH A WATER DISPERSION VARNISH BY ELECTROPHORESIS, THEN TREATING THE FILM COATING WITH A LIQUID SELECTED FROM THE GROUP CONSISTING OF AN ORGANIC SOLVENT AND A MIXED LIQUID OF WATER AND WATER-SOLUBLE ORGANIC SOLVENT, AND FURTHER COATING THE CONDUCTOR WITH A WATER-SOLUBLE VARNISH BY ELECTROPHORESIS, AND THEN BAKING THE COATED CONDUCTOR.
 2. The method of manufacturing insulated electric wire by electrophoretic coating an electric wire with a double coating film by applying an electrophoretic coating in a first electrophoretic bath, treating the coated wire in a treating bath of a liquid selected from the group consisting of an organic solvent, and a mixed liquid of water and a water-soluble organic solvent, and applying a second electrophoretic coating in a second electrophoretic bath. 